Meat Science 88 (2011) 117–121

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Effects of dry-ageing on pork quality characteristics in different genotypes Manuel Juárez a, William R. Caine a, Mike E.R. Dugan a, Nick Hidiroglou b, Ivy L. Larsen a, Bethany Uttaro a, Jennifer L. Aalhus a,⁎ a b

Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, Alberta, Canada T4L 1W1 Nutrition Research Division, Food Directorate, Health Products and Food Branch, Health Canada, Sir Frederick G. Banting Research Centre, Ottawa, Ontario, Canada K1A 0L2

a r t i c l e

i n f o

Article history: Received 10 December 2009 Received in revised form 25 May 2010 Accepted 2 December 2010 Available online 9 December 2010 Keywords: Genotype Ageing Purge loss Tenderness

a b s t r a c t Presumably, dry-ageing enhances flavour attributes of meat by surface desiccation to increase and modify fatty acid content and other organoleptic molecules. However information regarding dry-ageing of fresh pork is limited. To examine the effects of dry-ageing on pork quality, Large White (LW, n = 24) and Large White × Duroc (Duroc, n = 24) barrows were slaughtered and three longissimus thoracis et lumborum sections from each side of the carcass were wet or dry-aged for 2, 7 or 14 d. Dry-aged meat had lower (P b 0.001) moisture and higher (P b 0.001) protein content due to higher purge losses (P b 0.001) when compared with wet aged meat. However no dry-ageing effect (P N 0.05) was observed on sensory characteristics. The increase in the duration of ageing decreased moisture content and drip loss and increased (P b 0.001) protein content, purge loss and L*, chroma and hue values. These changes were more accentuated in dry-aged meat (P b 0.01). Days of ageing dependent increases (P b 0.001) were observed for instrumental and sensory tenderness and juiciness in both ageing types. Moreover, meat from Duroc barrows had lower (P b 0.001) moisture and protein content, and higher (P b 0.01) fat content, L* and hue values. Instrumental and sensory tenderness, juiciness and flavour were higher (P b 0.01) in meat from Duroc than LW barrows. Increases (P b 0.01) in flavour intensity and decreases in off-flavour of meat from LW barrows were greater (P b 0.05) in d 7 than in d 14. Therefore the duration of ageing affected most quality and sensory characteristics, while the changes to quality attributes of dry versus wet-aged pork were attributable to the differences in shrink losses in the present study. Crown Copyright © 2010 Published by Elsevier Ltd. on behalf of The American Meat Science Association. All rights reserved.

1. Introduction Adding value to fresh meat through post-slaughter processing is often founded on subjective sensory perception by consumers. Moreover retailers are constantly looking for ways to differentiate their products (Smith et al., 2008). In this context, based on the perception of improved flavour and tenderness (Campbell, Hunt, Levis, & Chambers, 2001; Warren & Kastner, 1992) many upscale restaurants dry-age beef before serving customers. However the effects of dry-ageing on flavour attributes are not clear (Parrish, Boles, Rust, & Olson, 1991). Dry-ageing is a traditional method of ageing beef, that involves direct exposure to air-flow and humidity in a cooler for a variable number of days followed by the trimming of spoiled or oxidized meat prior to cooking. This practice may be linked to shorter shelf-life because of bacterial growth, and higher shrink and drying out losses. In recent studies (Ahnström, Seyfert, Hunt, & Johnson, ⁎ Corresponding author. Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, Alberta, Canada T4L 1W1. E-mail address: [email protected] (J.L. Aalhus).

2006), dry-ageing in highly moisture-permeable bags has been demonstrated to increase yields and reduce microbial spoilage, without negative impact on product quality. In general, increasing wet-ageing (ageing in non-permeable, vacuum packaged bags) time has been reported to improve instrumental and sensory tenderness (Ellis et al., 1998; Juárez et al., 2009; Rees, Trout, & Warner, 2002), juiciness, flavour (Channon, Kerr, & Walker, 2004) and colour (Lindahl, Karlsson, Lundström, & Andersen, 2006) in pork. However, with the exception of cured ham, bacon or sausage aged after smoking or treating with salt or nitrites (Ai-Nong & Bao-Guo, 2005; Flores, 1997; Misharina, Andreenkov, & Vashchuk, 2001; Narváez-Rivas, Vicario, Constante, & León-Camacho, 2008) the information regarding dry-ageing of fresh pork is limited. Pork can suffer from excessive moisture losses and higher oxidative rancidity than beef, due to its higher levels of polyunsaturated fatty acids. Furthermore, the positive effects of ageing on quality characteristics in pork (e.g. texture and flavour) could be influenced by the level of fatness of the carcasses and the intramuscular fat content of the muscle, which is affected by pig genotypes. The focus of this study was to evaluate the effect of dry-ageing compared to conventional wet-ageing on objective and subjective

0309-1740/$ – see front matter. Crown Copyright © 2010 Published by Elsevier Ltd. on behalf of The American Meat Science Association. All rights reserved. doi:10.1016/j.meatsci.2010.12.011

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measures of pork loin quality from two genotypes differing in carcass and muscle fat composition. 2. Materials and methods 2.1. Animal management and slaughter processing Forty-eight barrows from two genotypes, Large White × Large White (LW, n = 24) and Duroc × Large White (Duroc, n = 24), were assigned on the basis of live-weight into pens of three animals at the Lacombe Research Centre Swine Unit. All pigs in the study were managed, handled and slaughtered in accordance with the principles and guidelines established by the Canadian Council of Animal Care (CCAC, 1993). The Large White breed was selected as a commonly used commercial breed. The Duroc breed was selected as a terminal cross for its greater overall fatness and propensity to increase marbling. Six weeks prior to slaughter the pigs received a finishing diet (Table 1). Pigs were given ad libitum access to feed and water. At 165 days of age, pigs were transported to the Lacombe Research Centre abattoir (0.5 km) for slaughter. At slaughter, final live weights were recorded and the animals were electrically stunned (400 V for 3 s), exsanguinated and dressed in a manner simulating commercial conditions. The processing of carcasses included pasteurization (16 nozzles at 12 L/nozzle for 10 s with 86.4 °C water for a total of 192 L/carcass) using an in-line stainless steel pasteurizing cabinet (Bryant, Brereton, & Gill, 2003). Following the splitting of the carcass, hot side weights were recorded. At 45 min post-mortem, the lean and subcutaneous fat thickness were determined on the left side of the carcass between the 3rd and 4th posterior ribs approximately 7 cm from the midline using a PG-100 Destron probe (Viewtrak Technologies Inc., Markham, ON, Canada). Both sides of each carcass were conventionally chilled in the cooler at 2 °C, with wind speeds of 0.5 m/s. At 24 h postmortem, the left and right sides of each carcass were weighed to determine total cooler shrink, and hot and cold dressing percentages were calculated. Fat hardness readings were recorded on both sides of each carcass between the 1st and 2nd thoracic vertebrae on the second subcutaneous fat layer using a Rex Durometer LG2400 (Rex Gauge Company, Buffalo Grove, IL, USA). 2.2. Composition and technological/instrumental pork quality traits The longissimus thoracis et lumborum (LTL) muscle was dissected from both sides of each carcass (24 h post-mortem) and the covering fat was trimmed to b12 mm in depth at any point on the surface of the loin. Each loin was cut into thirds. Sections were weighed and vacuum packaged into polyethylene (left loin sections) (Winpak, Winnipeg, MB, Canada) or moisture permeable (multiperforated film, average perforation spacing: 10 mm) polyamide thermoplastic elastomer (right loin sections) (Unipac, Edmonton, AB, Canada) bags for ageing. The packaged loin sections were stored on wire racks in a 1 °C cooler. Balancing for loin location at 2, 7 or 14 d post-mortem, a loin section from each animal and ageing treatment was removed from the cooler and weighed to determine purge loss

Table 1 Ingredients and analysis of diet. Ingredients Ground corn Ground peas Ground barley Canola meal Finisher pre-mixz Canola oil Selenium

g kg− 1 350.00 251.25 194.96 168.03 25.80 9.89 0.07

Composition −1

DE, Mcal kg Dry matter Crude protein Crude fat Crude fibre Lysine Calcium Phosphorus

g kg− 1 3.21 908.00 16.00 3.60 5.40 6.90 9.40 5.50

z Provided the following (g kg− 1): Protein, 110; Lipid, 24; Ca, 217; P, 22; K, 12; Mg, 39; S, 4.5; Na, 58.0; Co, 0.046; Cu, 0.66; I, 0.029; Fe, 5.28; Mn, 2.73; Zn, 5.45; Retinyl palmitate, 0.11; cholecalciferol, 1.63; dl-α-tocopheryl acetate, 1.37.

(muscle moisture loss during chilling period, which includes evaporative losses during dry-ageing). pH was then recorded at the anterior end of each section using an Accumet AP72 pH meter (Fisher Scientific, Mississauga, ON, Canada) equipped with an Orion Ingold spear-type electrode (Ingold Messtechnik, AG, Urdorf, Switzerland). Four 2.5 cm chops were cut from each loin section. The first chop was pre-weighed into a polystyrene tray with a dri-loc pad, over-wrapped with oxygen permeable film and stored at 1 °C for 48 h to determine gravimetric drip loss. The second chop was exposed to atmospheric oxygen for 20 min and instrumental colour measurements of L* (brightness), a* (red–green spectral axis), b* (yellow–blue spectral axis) were determined in duplicate using a Minolta CR-300 with Spectra QC-300 Software (illuminant C and 2° viewing angle; Folio Instruments, Kitchener, ON, Canada) as described by the Commission Internationale de l'Eclairage (CIE, 1978). The spectral values were used to calculate spectral colour (hue=arctan[b*/a*]) and colour saturation (chroma=[a*2 +b*2]0.5). The third chop was weighed and a spear point, copper-constantan thermocouple (10 cm in length; All Temp Sensors Inc., Edmonton, AB, Canada) attached to a Hewlett Packard HP34970A data logger (Hewlett Packard Co., Boise, ID, USA) was inserted into the center of the chop to monitor temperature during cooking. The chop was then grilled (Garland Grill ED30B; Condon Barr Food Equipment Ltd., Edmonton, AB, Canada) to an internal temperature of 34 °C, turned and cooked to a final internal temperature of 68 °C (Health and Welfare Canada, 1990). Upon removal from the grill, the total cooking time was recorded, the chop was weighed to determine cooking loss, then immediately placed into a polyethylene bag, sealed and immersed in an ice-water bath to prevent further cooking. After 20 min the chop was transferred to a cooler at 1 °C for 24 h. After chilling, chops were reweighed and then six cores (1.9 cm diameter) were removed from each chop. The peak shear force was determined on each core perpendicular to the muscle fibre using an Instron 4301 testing system (Instron Canada, Burlington, ON, Canada) with a Warner-Bratzler attachment and a crosshead speed of 200 mm/min. The remaining portions of the LTL sections were ground three times through a 3.2 mm grind plate and sub-samples were frozen at −20 °C. Following thawing soluble protein was extracted using phosphate-buffered potassium iodide and quantified using the biuret reaction as described by Barton-Gade (1984), with values expressed as grams of soluble protein per kilogram of lean muscle (Murray, Jones, & Sather, 1989). Moisture content was determined as the weight lost during heating 100 g of ground tissue at 102 °C for 24 h. After drying, samples were analyzed for crude protein (AOAC, 1995; Official Method 981.10) and crude intramuscular fat extracted with petroleum ether (AOAC, 1995; Official Method 991.36). 2.3. Sensory analysis of pork quality The fourth chop was vacuum-packaged in a polyethylene bag and frozen at −25 °C until all chops from the ageing process were available for sensory evaluation. Frozen chops were sorted by treatment to allow a balanced presentation of treatments to panellists. After thawing at 4 °C for 24 h the chops were cooked on a grill as previously described. Chops were sub-sampled by cutting 1.3 cm3 cubes from the centre of the chops taking care to avoid having an excess content of fat or connective tissue (AMSA, 1995). The cubes were placed in covered glass containers in a circulating water bath (68 °C) to equilibrate their temperature before being served to an eight-member sensory panel. Panellist training was based on published standards and guidelines (AMSA, 1995; ASTM International, 2009) with panellists previously extensively trained for the evaluation of meat. Chops were evaluated for initial and overall tenderness, amount of perceptible connective tissue, juiciness and flavour intensity using a nine-point descriptive scale, as follows: 9 = extremely tender, no perceptible connective tissue, extremely juicy and intense pork flavour; 1 = extremely tough, abundant connective tissue, extremely dry and bland pork flavour. All panel evaluations were conducted in well-ventilated, partitioned booths, illuminated by 180 lx green lighting. Distilled water and unsalted soda crackers were provided

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(2006), as ageing proceeds, shear force gradually decreases (P b 0.05), but beyond d 10, there is no further change in instrumental texture (P N 0.05). L* and hue values increased from d 2 to 14 (P b 0.001), while chroma increased from d 2 to 7 (P b 0.001). Similar results were found by Tikk, Lindahl, Karlsson, and Andersen (2008) related to the increases in oxymyoglobin and the decreases in myoglobin content. The extent and rate of oxygen diffusion into the meat surface has been reported to increase during ageing due to the continuous inactivation of oxygenconsuming enzymes (Lindahl et al., 2006; Tikk et al., 2008). The changes in moisture, protein content and drip and purge losses were more accentuated in dry-aged meat, as shown by the interactive effect between ageing time and ageing type (P b 0.01), due to its higher evaporative loss. Furthermore the increase in lightness over ageing time (L*) was more pronounced in meat from LW pigs (P b 0.05).

to cleanse the palate of residual flavour notes between samples (Larmond, 1977). 2.4. Statistical analysis Data were analyzed by Mixed Models procedures (SAS, 2003). The statistical model included genotype, ageing method and days of ageing as main effects, with slaughter group as random variable. When main effects were significant in the model (P b 0.05) linear contrasts with one degree of freedom were used for separation of least square means using the PDIFF option in SAS (SAS, 2003). Since most interaction effects were not significant (P N 0.05), only main effect means were shown in tables. Two-way interactions, when significant, were included in the tables (P value only) and discussed in the text. No three or four-way interactions were observed (P N 0.05).

3.3. Pork sensory characteristics

3. Results and discussion

It is well known that sensory attributes depend, among other factors, on genetic variations (Lawrie, 1991) and post-mortem treatment, including ageing (Meinert, Andersen, Bredie, Bjergegaard, & Aaslyng, 2007). In the present study, most sensory characteristics (Table 3) were affected by genotype (P b 0.05), mainly due to the differences in intramuscular fat (Lindahl et al., 2006). However, no genotype by ageing type interaction (P N 0.05) was observed for sensory traits. Dry-ageing increased cook time and decreased cook loss (P b 0.001), as reported by Laster et al. (2008) in dry-aged beef. Lower moisture content may lead to a slower rate of heat transfer. However no difference in sensory characteristics was detected between wet and dryaged pork (P N 0.05). When dry-ageing was studied in beef, no significant differences for sensory traits were detected (Parrish et al., 1991), and consumers were unable to determine differences between dry- and wet-aged steaks (Smith et al., 2008). On the other hand, other authors have reported increases in tenderness (Richardson, Nute, & Wood, 2008) and improvements to flavour (Campbell et al., 2001) in dry-aged beef, possibly due to the differences in lipid and protein oxidation during ageing and the subsequent formation of volatiles during cooking. Sitz, Calkins, Feuz, Umberger, and Eskridge (2006) reported that depending on steak grade, wet-ageing had null or positive effects on consumers’ preference, indicating that high quality beef can be wet-aged with desirable palatability results. In the present study, after observing the differences in moisture, protein, drip and purge loss between dry and wet-aged pork, significant effects on pork surface oxidation and sensory traits could be expected. However, the lack of effect on palatability may be partly explained by the use of official methodologies for sensory analysis. According to AMSA (1995), after cooking, samples for the sensory analysis were collected from the centre of the chop to avoid heterogeneous results from outside areas which

3.1. Growth and carcass characteristics Similar to the results reported in a previous study (Juárez et al., 2009), Duroc cross barrows in the present study had higher final weight and hot carcass weight (data not shown; P b 0.01). These results were expected since Duroc pigs have been reported to grow faster and have a better feed conversion ratio than pigs of other breeds (Blanchard, Warkup, Ellis, Willis, & Avery, 1999; Latorre, Medel, Fuentetaja, Lázaro, & Mateos, 2003; Young, 1992). However, no differences (data not shown; P N 0.05) in other carcass traits were observed among genotypes. 3.2. Compositional and instrumental quality characteristics Crossbreeding with Duroc increased (P b 0.001) LTL intramuscular fat content by 48.9% (Table 2). The intramuscular fat increase in pork from Duroc genotype has been widely reported (Channon et al., 2004; Edwards, Bates, & Osburn, 2003; Ellis et al., 1998) and it has been correlated to lower shear force values and higher L* and hue values (Juárez et al., 2009). However, no interaction was observed between the genotype and ageing type in the present study (P N 0.05). Dry-ageing decreased moisture content and drip loss and increased protein content and purge loss (P b 0.001). These effects have been reported by several authors in dry-aged beef (Ahnström et al., 2006; Campbell et al., 2001; Laster et al., 2008; Warren & Kastner, 1992) and dry-aged cured pork products (Carrapiso & García, 2008; Ramírez & Cava, 2007). As ageing progressed, decreased moisture content and drip loss and increased pH, protein content and purge loss (P b 0.001) were observed in both ageing types. As reported by Ellis et al. (1998), increasing ageing time also decreased shear force values (P b 0.001). According to Xiong et al.

Table 2 Main effect means for pork quality characteristics from barrows differing in genotype, ageing type and days of ageing (n = 48). Genotype

pH Moisture, mg g− 1 Protein, mg g− 1 Fat, mg g− 1 Sol. Prot., mg g− 1 Drip loss, mg g− 1 Purge Loss, mg g− 1 Shear, kg L* Chroma Hue

Aged z

SEMy

Day

Duroc

LW

Dry

Wet

2

7

14

5.61 725.13 244.14 28.65 189.82 31.22 60.72 5.27 55.50 11.26 35.41

5.61 731.23 247.42 19.25 205.33 31.64 60.11 5.79 54.15 10.90 33.29

5.62 722.02 251.26 24.57 200.81 23.36 96.12 5.54 54.75 11.16 34.67

5.60 734.34 240.31 23.33 194.33 39.51 24.66 5.52 54.90 11.01 34.02

5.57b 736.21a 239.47c 23.01 195.11 43.73a 22.45c 6.13a 53.61c 10.27b 30.69c

5.63a 728.84b 243.00b 24.37 197.48 31.13b 60.79b 5.40b 54.91b 11.30a 34.47b

5.62a 719.48c 254.88a 24.48 200.13 19.44c 98.00a 5.07c 55.96a 11.68a 37.87a

0.02 1.10 0.56 1.56 2.67 2.97 1.29 0.10 0.28 0.15 0.48

Sig.x Genotype

Aged

Day

G*Dw

A*Dv

ns *** *** *** *** ns ns *** *** ns ***

ns *** *** ns ns *** *** ns ns ns ns

*** *** *** ns ns *** *** *** *** *** ***

ns ns ns ns ns ns ns ns * ns ns

ns *** *** ns ns ** *** ns ns ns ns

LWz = Large White; SEMy = Standard error of least square means; Interactions: Sig.x: Significant differences. ns = P N 0.05; * = P b 0.05; ** = P b 0.01; *** = P b 0.001; G*Dw = genotype and days; A*Dv = ageing and days. a, b, c : means with different letters are statistically different (P b 0.05).

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Table 3 Main effect means for pork sensory characteristics from barrows differing in genotype, ageing type and days of ageing (n = 48). Genotype Duroc −1

Cook time, sec g Cook loss, % Initial Tenderness Juiciness Pork Flavour Intensity Off Flavour Intensity Connective Tissue Overall Tenderness

7.63 22.81 6.14 4.70 4.77 7.39 8.07 6.57

Aged LWz 7.92 23.68 5.86 4.48 4.63 7.28 8.09 6.28

Dry 8.11 21.99 6.03 4.63 4.66 7.33 8.07 6.44

SEMy

Day Wet 7.44 24.50 5.97 4.56 4.74 7.34 8.09 6.40

2

7 b

7.31 25.02a 5.50c 4.39c 4.62b 7.30ab 7.98b 6.09c

14 b

7.69 23.28b 6.10b 4.58b 4.79a 7.43a 8.10a 6.50b

a

8.33 21.43c 6.40a 4.81a 4.69ab 7.27b 8.16a 6.68a

0.22 0.41 0.18 0.09 0.03 0.11 0.05 0.17

Sig.x Genotype

Aged

Day

G*Dw

A*Dv

ns ** *** ** ** * ns ***

*** *** ns ns ns ns ns ns

*** *** *** *** ** * *** ***

ns ns ns ns * ns * ns

** *** ns ns ns ns ns ns

LWz = Large White; SEMy = Standard error of least square means; Interactions: Sig.x: Significant differences. ns = P N 0.05; * = P b 0.05; ** = P b 0.01; *** = P b 0.001; G*Dw = genotype and days; A*Dv = ageing and days. Sensory characteristics were rated using a nine point descriptive scale, as follows: initial and overall tenderness (9 = extremely tender; 1 = extremely tough), juiciness (9 = extremely juicy; 1 = extremely dry), flavour intensity (9 = intense pork flavour; 1 = bland pork flavour), off-flavour intensity (9 = no off-flavour; 1 = extremely intense offflavour), connective tissue (9 = no perceptible connective tissue; 1 = abundant connective tissue).

may have been cooked to different endpoints. Given our objective results, the drying and concentration of flavour compounds may have been higher in the outside areas which were removed before being served to panellists following official guidelines. In future studies, alternative sampling methodologies could be used to try to evaluate the sensory effects of dry-ageing on the surface. Moreover, in this study, the level of dl-α-tocopheryl acetate in the diet (Table 1), similar to those used in commercial diets, may have altered the oxidation rate of aged meat, decreasing the impact of dry-ageing on flavour and in turn reducing the differences between dry and wet-aged pork. However, the shrink and trim losses associated with dry-ageing were higher than for regular wet-ageing, increasing the price per unit weight of dry-aged meat. Increasing the days of ageing increased cooking time and decreased cook loss (P b 0.001), especially in dry-aged meat (P b 0.001) due to earlier moisture losses. Initial and overall tenderness and juiciness increased from d 2 to 14 (P b 0.001), flavour intensity increased (P b 0.01) and the amount of connective tissue perception decreased (P b 0.001) from d 2 to 7, and off-flavour intensity increased from d 7 to 14 (P b 0.05). According to Meinert et al. (2007), ageing increases the concentration of flavour precursors, responsible for forming the characteristic meat flavour during cooking. Moreover Ellis et al. (1998) observed that tenderness increased from 2 to 16 d (P b 0.05), but not from d 2 to 9 (P N 0.05). The effects on flavour intensity and connective tissue were more accentuated (P b 0.05) in meat from LW barrows, as indicated by the interactive effect between the genotype and days of ageing. 4. Conclusions As expected, pork tenderness and palatability increased during ageing, and the differences in intramuscular fat content among breeds affected sensory characteristics. However, according to the results obtained in this study, the increased purge loss in dry-aged loin chops was not compensated by significant improvements in pork flavour or tenderness attributes assessed by trained panellists using the standard guidelines. Moreover, the differences in intramuscular fat content among genotypes did not result in different effects from dry-ageing in pork quality traits. Acknowledgements Financial support was provided by Agriculture & Agri-Food Canada. The assistance in managing and transport of the pigs provided by Sheri Nelson, Shane Sroka, Jim Rudy and Michelle Hambly is sincerely appreciated. Excellence in skill and adherence to a timed slaughter and meat processing schedule by Chuck Pimm, Darcy Schatschneider, Dwight Baird, Darryl Pierce and Jeremy Sealock of the Lacombe Meat Centre is also appreciated. The authors also wish to thank the dedicated

technical assistance of Stan Landry, Rhona Thacker, Fran Costello, Lorna Gibson, Christine Burbidge-Boyd and Glynnis Croken.

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